Vigils are to be staged across the UK by anti-Iraq war groups to mark the death of the 100th British soldier since the conflict began in 2003.
Anti-Iraq war groups marked the 100th death outside Parliament
Stop the War Coalition supporters turned up in Parliament Square on Tuesday ahead of the nationwide events.
Respect MP George Galloway and former Labour MP Tony Benn were among those who read out the names of all the dead.
Prime Minister Tony Blair said the death was a "tragedy" but troops would remain in Iraq for as long as needed.
He told the BBC: "It is important because what is happening in Afghanistan and Iraq is that the people of those countries want to leave behind terrorism and extremism and they want to embrace democracy."
The Ministry of Defence said the latest soldier to die in Iraq was Corporal Gordon Alexander Pritchard, 31, from the Royal Scots Dragoon Guards, who was killed in a blast in Umm Qasr, Basra province on Tuesday.
His death follows that of Lance Corporal Allan Douglas, 22, who died on Monday.
UK CASUALTIES IN IRAQ
100 service personnel killed
77 died in action
23 from non-combat injuries
Defence Secretary John Reid said the 100th death called for a reflection of the contribution British servicemen and women had made to international stability.
He said it was an appropriate time to reflect on the "dedication, courage, professionalism and sacrifice" of the armed forces and their families.
Cpl Pritchard's parents Jenny and Bill said he was "the epitome of a modern, professional soldier" and "extremely proud" of his regiment.
In a statement they said the married father had followed family tradition by serving with the Royal Scots Dragoon Guards.
The family of L/Cpl Douglas, who was shot and killed in Maysan province on Monday morning, said he had not wanted to return to Iraq.
Diane Douglas told the BBC it was a "damn disgrace" that young people were being killed in Iraq, adding: "I don't think Tony Blair should have put any young kids out there."
Wooden crosses with red poppies were placed in the turf in Parliament Square during Tuesday's vigil to mark the 100th death.
Rose Gentle, whose son Gordon was killed in Iraq in 2004, will be at a protest in Glasgow on Wednesday.
"We just want to let other families know that they are not alone and everyone there will be thinking about them and concerned about how they are feeling," Mrs Gentle, a member of the Military Families Against the War group, said.
"I hope people will come out to the vigils and speak out against the war to help us bring the troops home before any more boys are killed," she added.